Unbalance measuring apparatus



April 25, 1961 J, F LASH 2,981,112

UNBALANCE MEASURING APPARATUS Filed NOV. 30, 1955 INVENTOR ATTonNEYUNBALANCE MEASURING APPARATUS Joseph F. Lash, Ferndale, Mich., assignerto General Motors Corporation, Detroit, Mich., a corporation of DelawareFiled Nov. 30, 1955, Ser. No. 550,035

2 Claims. (Cl. 73--462) This invention relates to apparatus formeasuring the amplitude and location of unbalance in a rotating bodyandhas for its general object to provide a unique, extremely simple andyet versatile apparatus for performing such measurements.

In distinction to prior forms of unbalance measuring apparatus using astroboscopic ash lamp, a reference alternator or adjustable commutatordevice for determining the angular location of unbalance in a workpiece,the present invention features a unique phase disk arrangement andadjustable, electrical pickup for this purpose and accomplishes suchmeasurements with `an extremely simple apparatus using a minimum nu-mberof parts. Y

The invention, both as to its organizationA and operation, will appearmore fully from the following description and drawings, wherein:

Fig. 1 is a diagrammatic illustration of the general organization of anunbalance measuring apparatus using the phase disk of the presentinvention; and

Figs. 2 and 3 areviews of alternative forms of phase disks that may beemployed in the apparatus of Fig. 1.

The invention is shown in a balancing machine in which the part 10,whose characteristics of unbalance are to be determined, is mounted on avertically disposed, flexibly mounted spindle 12 which is driven by aconstant Vspeedelectrical drive motor 14 having a hollow drive lshaft16.*, The motor 14 is adapted to be connected over conductors 18, 20through a switch 22 to a suitable source of electrical power. Themachine spindle 12extends coaxially through thehollow drive shaft of the:motor and is connected at its lowermost end to the lower .end ofthedrive shaft16 through a universal joint or connection, in known manner.The uppermost-portion of the balancing-machine spindle is resilientlysupported i in a spring mounted bearing 26 which permits oscillaparatusof Fig. l are shown in block diagrammatic form with theirinterconnections shown in single line, diagrammatic form, the remainingconnection for each of which being connected to ground for completingtheir individual circuits. The output from the pickup 28 is applied overline 36 to the input of a conventional amplitier 40. The output of theamplifier is in turn connected over line 42 to a full-wave rectifiershown at 46 which may be of the electronic vacuum tube or dry-typevariety or of the mechanical variety. The output of the rectitier isconnected over line 48 to a conventional D.C.

' indicating instrument shown at 52.

tion or deiiection of the balancing machine spindle under a theinfluence ofA unbalance in the workpiece.

*Suitably mounted in contacting relation the machine spindle 12 orbearing 26 is 'the movable iprobe 30 ofanelect'ro-dynamic 'pickuptransducer 2,8k having a away from the casingl This currentjwillbejaj/sin'us-V oidal signalshownuby the curve a. Thissignalfwillhaver a1frequency: 'corresponding vto the speed ofthe drive motor, andanamplitude in accordance with the amount of unbalance in thek `workpieceasdetermined bythe In accordance with the present invention there isincluded in the balancing organization above described, a phase disk 56,which is mounted on and rotates with the shaft 1-6 of the drive motor, aradially positionable magnetic pickup 60, which cooperates with thephase disk to produce a reference signal having a known phase relationwith respect to the said fixed point on the spindle, and a suitable wavegenerating means 62, which may be of the electronic variety.

The phase disk 56 may be constructed of steel, for example, and may beperforated with a number of holes 64 which are spaced an equal number ofdegrees apart, with each successive hole being at a slightly differentradius from the center of the disk so as to define collectively agenerally spiral-shaped curve, such as an Archimedean spiral, in whichthe increment of increase in successive radii is constant. The magneticpickup 60, which may be of most any commercially available variety, ismounted on an axially translatable push rod 66 supported between a pairof spaced bracketsy 68 and 70 and is provided with a push knob or button72 at its end opposite the pickup 60. The rod 66 also carriesintermediate its ends an indicator or pointer 74 that cooperates with astationary, uniformly graduated indicia plate '76 which may b e mountedon a stationary part of the balancing machine. The scale is uniformlyand linearly calibrated, and each graduation thereon may correspond tothe radial position of a particular hole in the disk so that the probemay be located at a radial position corresponding to any hole. i

Theoutput of the pickup 60 is rshown at b as a periodically occurringpulse having a repetition rate corresponding tothe speed of the spindleand is applied over a symmetrical square wave, such as is shown at c,hav- Ving equal on-oif half-periods and a total period or reptition ratecorresponding to the speed of the drive spindle.

yThe output of the wave generator 62 is applied over line 84 through anadjustable attenuator 86 tothe `input of.y

the ampliiier 40 where it is combnedlwithkthe output of the pickupdevice 28, j n x By adjusting the rod 66`in and out radially-of thedisk,

"the phase relationshipvbetweenthe` square wave genamount of deection ofthe balancing `-machine spindle in n.

aihorizontalplane containing the ymovable probe vof the pickup.' Theelectrical signal'developed by the pickup -will'bear avariable phaserelationshipwith respect to a lixed point :on the spindle or workpiece.yThe various elements of the electrical measuring ap- `erated'by thegenerator 62 and the unbalancesine wave V--developed by `the` pickup 28can be varied. When the probe is adjusted so-that thef square fwave isapproximately in phase with" the unbalance signal, the meter 52 willreadA afmaxin'ium.l -vWhern these signals are 180 degreesout of phase,theL meter will-read afminiinum. lf

' there is, no unbalancev'in the workpiece 1l), themeter readingwillremain unchanged as theprobe scans the disk.

The position, of the probe when a ymaximum or` minimum has been found,indicates the location of the unbalance which may be read from theposition of the indicator 7d relative to the graduated indicia on theindicator plate 76. Where the amplitude of the unbalance signal is lessthan that of the attenuated square wave reference signal, the dilerencebetween maximum and minimum meter readings will be twice the amplitudeof unbalance. The magnitude of unbalance also could be indicated byopening switch 89 and applying only the output of the unbalance pickup23 to the amplifier, rectier and meter.

it is, of course, apparent that there are numerous other means by whicha reference signal may be obtained from the phase disk 56. The disk maybe provided with a reference marker of any suitable'type that willcooperate with the pickup' 6i) toproduce a reference signal. Forexample, in Fig. 2 the-disk is slotted as shown at 9d with the spacedwalls of the slot being shaped to conform to a 360 degree segment of anArchimedean spiral. The continuous slot enables the magnetic pickup toscan a continuous range of angular positions of the disk. As a furtheralternative, the spiral strip 92 of magnetic material may be provided ona non-magnetic disk to actuate a magnetic pickup.

While electronic resolving circuits and the like could be employed toprovide an electronic wave generator having a sinusoidal output, thesquare wave multivibrator appears to be the simplest, least expensive,electronic device that could be employed 'for the wave generating means62. employed in the present invention. Since the square wave will have afundamental frequency component corresponding to the frequency of theunbalance pickup signal, this component may be mixed or combined readilywith the unbalance signal to produce a resultant signal whose amplitudewill vary sufhciently and enable determining the magnitude and thelocation of the unbalance in accordance With the principles of thepresent invention. Where the output of the magnetic pickup is ofsuicient energy, the wave generating means 62 might be eliminated andthe output of the magnetic pickup could be combined directly withl theunbalance pickup signal.

The above described apparatus for indicating unbalance has been foundwell suited for use in multi-station type balancing installations havinga final check or inspection station for performing a iinal inspectionfor any remaining unbalance after the parts have been corrected. Abalancing installation of this character isdisclosed in copending U.S.application Serial No. 550,151, now Patent No. 2,898,764, led November30, 1955, inthe names or" C. I. Kinsey and J. H. Varterasian and ofcommon ownership herewith. The check station would normally have anunbalance pickup, amplifier, Arectiiier and a passreject relay. In suchinstallations it is good practice toinspect occasionally the balance ofthe spindle vkat the inspection station with a master part to determinethe magnitude and the location ofany residual unbalance Vthat might belfound in order that the vsystem will be properly calibrated.r Theapparatus described conveniently Vprovides this information' simply bythe addition of the phase disk, `magnetic probe and the one-shotmulti-vibrator.

While vthe apparatus has'beenjdescribed in connection 'y with'a'rbaiancing machine in which the characteristics of nnbalance` areydetermined in a single transaxialplane ofv a workpiece, the apparatuscan, of course, be employed Y withother forms of balancingapparatusincluding Vdynamic baiancing machines for balancing ofaxiallyelongated Y worlpieces, the characteristics of unbalance of which are tobe determined in a plurality of spaced transaxial n planes.. i

What is claimed is:

l. In an unbalance indicating system for determining the magnitude andthe location of unbalance in a rotatable workpiece including afiexibly-mounted drive spindle supporting said workpiece, a drive motorhaving a shaft coupled to said spindle, an unbalance pickup devicecontacting said spindle and developing an electrical unbalance signalhaving characteristics related to the magnitude and the location ofunbalance in said workpiece, a phasedisk driven yfrom the shaft of Saiddrive motor and having a spiral slot emanating radially outwardly fromthe center Ithereof, a magnetic pickup adjustably positionable radiallyof said disk and developing a reference signal pulse each time analigned portion of said slot passes' thereby, means connected -to saidmagnetic pickup generating an electrical Wave synchronized by the signalpulse from the magnetic pickup and having a period corresponding to theinterval between successive pulses therefrom, means combining saidelectrical wave from said wave generating means with said unbalancesignal from said unbalance pickup device, rectifying means connected tosaid last-named means, first indicating means connected to saidrectifying means for indicating the average relative value of thevectorial sum oi said unbalance signal and said electrical wave, andsecond indicating means connected to said magnetic pickup for indicatingthe radial position thereof with respect to the center of said disk,said'radial position having a predetermined relation to the angularlocation of said aligned portion of said slot.

2. An unbalance indicating system for determining the unbalance in aworkpiece, said system comprising means for rotatably driving saidworkpiece and including a phase disk driven in synchronous relation tosaid workpiece, an unbalance pickup responsive -to vibrations from saidlworkpiece to produce` an unbalance signal indicative of the amplitudeof the unbalance and having a predetermined phase relationship to theangular position of said unbalance, said disk having a spirally arrangedreference marker, emanating radially outward from the center thereof,the radial location of any point on said marker having a predeterminedrelationship to the angular location thereof with respect to a fixedpoint on said disk, a radially movable reference pickup for radiallyscanning said phase disk and cooperating with said marker to produce areference signal having a phase relationship with respect to said fixedpoint dependent on the radial position of`said reference Vpickupfmeansfor comparing said unbalance signal and said reference signal todetermine the phase relationship between said signals, and means forindicating the radial position of said reference pickup when saidsignals havey a'predetermined phase relation. Y K Y References Cited inthe file of this .patent `UNITED STATES PATENTS Y 2,050,073 Thearie Aug;4, 1936 A 2,198,624 The'arle i- Feb. 15,51938 2,243,457 Esval May 27,1941 2,243,458, Esval May 27,1941 2,403,513 Forsberg July 9, 1946V2,405,430',y nenty Au'g s, 1946 2,426,305 y 'Hope Aug."26, y19472,500,013, e' Svensson vMar. l, 1950 *2,622,437v Frank Dec. 23, 19522,636,381 jHagg JApr. V28, '1953 2,730,899 Hellar et al.A Y Jan.v17j-1956 g' Y vPensioninrierrrs 91,385 v Q-,"filitzerland Y 4 V Nov. 1',`1921 474,673

Great Britain 1 Nov. 1., 193.7

